Characterization and Application of Lanthanide-Binding Proteins for Rare-Earth Separations

Mattocks, Joseph

Characterization and Application of Lanthanide-Binding Proteins for Rare-Earth Separations

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Author:: Mattocks, Joseph
Graduate Program:: Chemistry
Degree:: Doctor of Philosophy
Document Type:: Dissertation
Date of Defense:: June 16, 2022
Committee Members:: Joseph Cotruvo, Chair & Dissertation Advisor
Scott Lindner, Outside Unit & Field Member
Philip Bevilacqua, Major Field Member
Squire Booker, Major Field Member
Philip Bevilacqua, Program Head/Chair
Keywords:: Rare earth element
Lanthanide
Protein
Separation
Bioremediation
Extraction
Abstract:: The lanthanides (Z=57-71), plus scandium and yttrium (Z=21, 39), comprise the rare earth elements (REEs) – a group of 17 elements that perform irreplaceable functions within diverse technologies such as semiconductors, phosphors, medicines, electronics, and green technologies. Due to their similar physicochemical properties, resulting from their uniform trivalent oxidation states and similar ionic radii, REEs co-occur in geologic deposits, necessitating resource-intensive and environmentally harmful refinement processes for both their extraction and recycling. Therefore, development of greener and more efficient processes for REE recovery and separation is a topic of intense interest, additionally spurred by the geopolitical reality that the U.S. relies on China for sourcing and processing of the vast majority of its REEs. Our recent discovery of the lanthanide-binding protein, lanmodulin (LanM), represents both a window into Nature’s strategies for REE recognition and a possible solution to some of these complexities. LanM is the tightest binding and most selective naturally occurring macrochelator of REEs and actinides known. In this thesis, we develop and apply titration methods to characterize LanM’s conformational response with the whole range of REEs, under a variety of solution conditions, and use these methods in conjunction with other biophysical methods to begin to understand the interplay between metal site structure and conformational response in determining LanM’s selectivity for and among REEs and actinides. We use LanM as the basis for a selective, genetically encoded fluorescent sensor for lanthanides (LaMP1), which demonstrates selective cytosolic uptake of light lanthanides in methylotrophic bacteria for the first time. We also optimize a version of LanM that can be efficiently immobilized and take advantage of the protein’s reverse-size selectivity relative to conventional chelators to allow for an efficient chromatographic separation of REEs that outperforms many existing technologies. Finally, we explore the unifying features as well as diversity within the lanmodulin family of proteins by characterizing a homologue of LanM and use a host of biophysical methods to reveal a novel protein dimerization that occurs selectively in the presence of light REEs, an observation with exciting implications for further development of protein-based technologies for REE sensing, recovery, and separation.

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